104 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



2. DETERMINATION OF RESIDUAL CARBON DIOXID. a 



Weigh 2 grams of baking powder into a flask suitable for the subsequent deter- 

 mination of carbonic acid, add 20 cc of cold water, and allow to stand 20 minutes. 

 Place the flask in a metal drying cell surrounded by boiling water, and heat with 

 occasional shaking for 20 minutes. 



To complete the reaction and drive off the last traces of gas from the semisolid 

 mass, heat quickly to boiling over a lamp, and boil for one minute. Aspirate until 

 the air in the flask is thoroughly changed, and determine the residual carbon dioxid 

 by absorption, as described under total carbonic acid. 



The process described, b based on the methods of McGill c and Catlin, d imitates as 

 far. as practicable the conditions encountered in baking, but in such a manner that 

 concordant results may be readily obtained on the same sample, and comparable 

 results on different samples. 



3. DETERMINATION OF AVAILABLE CARBON DIOXID. 

 Subtract the residual carbon dioxid from the total. 



4. DETERMINATION OF ACIDITY. 



(For cream of tartar and its substitutes.) 



Dissolve one gram of the material in hot water and titrate with standard fifth- 

 normal potassium hydroxid solution, using phenolphthalein as indicator. 



5. DETECTION OF TARTARIC ACID, FREE OR COMBINED. e 

 Applicable in presence of phosphates. 



Shake repeatedly about 5 grams of the sample with about 250 cc of cold water in a 

 flask and allow the insoluble portion to subside. Decant the solution through a 

 filter and evaporate the filtrate to dryness. To the dry powdered residue add a few 

 drops of a 1 per cent solution of resorcin and about 3 cc of strong sulphuric acid. 

 Heat slowly. A rose-red color indicates tartaric acid, the color being discharged on 

 dilution with water. 



6. DETECTION OF FREE TARTARIC ACID. 



Extract 5 grams of the powder with absolute alcohol and evaporate the alcohol 

 from the extract. Dissolve the residue in dilute ammonia, transfer to a test tube, 

 add a good-sized crystal of silver nitrate, and heat gently. Tartaric acid is indicated 

 by the formation of a silver mirror. If desired, the absolute alcohol extract may be 

 tested by the Wolff method, as described under 5. 



7. DETERMINATION OF TOTAL TARTARIC ACID. f 



The following is the Goldenberg-Geromont-Heidenhain method, applicable only in 

 the absence of aluminum salts, calcium salts, and phosphates: 



Into a shallow porcelain dish, 6 inches in diameter, weigh out 2 grams of the 

 material and sufficient potassium carbonate to combine with all tartaric acid not in 

 the form of potassium bitartrate. Mix thoroughly with 15 cc of cold water and add 

 5 cc of 99 per cent acetic acid. Stir for half a minute with a glass rod bent near the 

 end. Add 100 cc of 95 per cent alcohol, stir violently for 5 minutes and allow to 

 settle at least 30 minutes. Filter on a Gooch crucible with a thin layer of paper 

 pulp, and wash with 95 per cent alcohol until 2 cc of the filtrate do not change the 



See Appendix, p. 157. 



fcConn. Agr. Exp. Sta. Rep., 1900, p. 169. 



Lab. Inland Rev. Dept., Ottawa, Canada, Bui. 68, p. 31. 



d Baking powders. A Treatise on the Character, Methods for Determination of the Values, etc. , p. 20. 



Wolff, Rev. ehim. anal, appl., 1899, 4, 263. 



f See Appendix, p. 158. 



